As well known, shutting off devices in said braking systems operate to shut off the damaged section or sections from the supply or power circuit, while allowing the compressor to supply the remaining undamaged sections.
Prior art shutting off valves are usually of the one seat type. When a section becomes damaged, air is continuously vented to atmosphere, which causes a pressure drop and oscillation in the tanks and other sections of the system, which is prejudicial to braking efficiency.
Devices are also known for avoiding the above mentioned disadvantage. Such devices use variable area valves, which provide a restricted passage area to the damaged section hindering at the recharging step the violent air flows from the undamaged sections. However, such approaches require an undue accuracy in clearance between the valve seat and plug and its effectiveness is substantially problematical.
It is another disadvantage of prior art valves that in a system provided with a plurality of shutting off valves, it would be substantially impossible to provide and maintain in time identical calibrations for all of the valves.
It may occur that, should the section controlled by the valve of lowest calibration become damaged, the entire flow from the compressor would escape from said damaged section, and the other sections could not be recharged.